Paint composition for concrete and masonry surfaces

ABSTRACT

The present invention is directed to a water-based paint composition for concrete and masonry surfaces, a method of coating a concrete or masonry surface, and a corresponding method of preparing a coated concrete or masonry surface. The paint composition includes about 10-50% by weight water, about 5-40% by weight colloidal silica particles, about 40-85% by weight of an inorganic pigment, and about 1-10% by weight of a polymer binder. The paint composition provides the coated surfaces with excellent resistance to a wide variety of weather conditions, and alleviates health and safety concerns associated with long-term exposure to conventional organic-based paints.

FIELD OF THE INVENTION

This invention is directed to a water-based paint composition designedfor application to concrete and masonry surfaces. The paint compositionhas excellent weathering resistance and anti-fungal properties andalleviates the environmental and health concerns associated withorganic-based paint compositions. The invention also includes a methodfor coating concrete and masonry surfaces, and a method for preparing acoated concrete or masonry surface.

BACKGROUND OF THE INVENTION

Organic-based paint compositions, such as latex paints, haveconventionally been used for coating concrete and masonry surfaces. Mostof these applications are in outdoor environments, or industrial indoorenvironments, and require prolonged resistance to extreme environmentalconditions. While organic-based latex paints have performed well inthese applications, they are relatively expensive due to theirpredominantly organic chemical compositions. Also, prolonged exposure tolatex paints either before coating, or after coating and before drying,raises health and safety concerns especially in indoor environments.

Water-based paint compositions are less expensive and moreenvironmentally safe. However, conventional water-based paintcompositions have not provided suitable long-term resistance to weatherand other extreme conditions. Also, conventional latex-based andwater-based paint compositions can show signs of mold or fungal growthover time, if the applied surfaces are exposed to wet or humidconditions.

There is a need or desire for a relatively inexpensive paint compositionthat provides long-term resistance to weather and extreme conditions,resists mold and fungal growth, and is free of health and safetyconcerns.

SUMMARY OF THE INVENTION

The present invention is directed to a water-based paint composition forapplication to concrete and masonry surfaces. The paint compositiongenerally includes about 10-50% by weight water, about 5-40% by weightcolloidal silica particles, about 40-85% by weight of an inorganicpigment, and about 1-10% by weight of a polymer binder. The paintcomposition may also include about 0.1-5% by weight of an anti-fungalingredient and about 0.01-2% by weight of a synthetic or natural gum.Suitably, the paint composition does not include more than about 10% byweight of all organic components, inclusive of the polymer binder.

The water-based paint composition has excellent weathering resistanceand does not wash away, fade or peel when a coated concrete or masonrysurface is exposed long-term to a wide variety of weather conditions.The water-based paint composition also alleviates or avoids theenvironmental and health concerns associated with long-term exposure anduse of organic-based paint compositions.

The invention also includes a method of coating a concrete or masonrysurface. The method includes the steps of providing a water-based paintcomposition including water, colloidal silica particles, and organicpigment and not more than about 10% by weight of a polymer binder;applying the water-based paint composition to a concrete or masonrysurface; and evaporating the water from the paint composition. Theinvention also includes a corresponding method of preparing a coatedconcrete or masonry surface.

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed to a water-based paint composition that isfree of health and safety concerns, environmentally safe, inexpensive,and designed to provide a long-term weather-resistant coating forconcrete and masonry surfaces. The paint composition includes about10-50% by weight water, suitably about 15-40% by weight or about 20-30%by weight. The paint composition also includes about 5-40% by weightcolloidal silica particles (based on dry weight), suitably about 10-30%by weight or about 15-25% by weight. The colloidal silica particles areadded to the other ingredients of the paint composition as an aqueouscolloidal suspension including about 30-50% by weight colloidal silicaparticles and about 50-70% by weight water, suitably about 40% colloidalsilica particles and about 60% by weight water. The water from thecolloidal dispersion is counted as part of the overall water content inthe paint composition, stated above.

An aqueous colloidal silica suspension is defined as including silicaparticles with diameters of 10⁻⁷ to 10⁻⁹ meters (about 1-100 nanometers)suspended in a continuous water phase. The mixture has propertiesbetween those of a solution and a fine suspension. Colloidal silicaparticles are defined as silica particles within the colloidal sizerange, having diameters of about 1-100 nanometers, suitably about 4-100nanometers, or about 6-50 nanometers, or about 8-20 nanometers.

The paint composition includes about 1-10% by weight of a polymerbinder, suitably about 2-8% by weight, or about 2-5% by weight. Thepolymer binder, which also provides flexibility to the paint compositionto prevent peeling, can be a polymer or copolymer of acrylic,acrylamide, vinyl ethers, vinyl esters, urethanes, methacrylates, andepoxy esters. One suitable binder polymer is a styrene-acrylatecopolymer available from BASF Chemical Co. under the product nameACRONAL® NX4627X. This product is an aqueous emulsion containing 47-49%by weight styrene-acrylate polymer solids and 51-53% by weight water,the latter being counted as part of the overall water content of thepaint composition stated above. Otherwise, the polymer binder can beprovided in a mixture including about 35-60% by weight of the polymerbinder and about 40-65% by weight of the water.

Because objectives of the paint composition include minimizing cost,health and safety concerns, the total amount of all organic componentsin the paint composition suitably does not exceed about 10% by weight,including the binder polymer. The binder polymer may be the only organiccomponent.

The paint composition includes about 40-85% by weight of an inorganicpigment, suitably about 45-80% by weight, or about 50-80% by weight. Theinorganic pigment is suitably in the form of very fine particles havingdiameters of about 0.1-100 microns, suitably about 0.2-70 microns.Suitable inorganic pigments include without limitation aluminum oxide,silicon oxide, titanium dioxide, zinc oxide, iron oxide, graphite,antimony oxide, chromium oxide, cobalt aluminum oxide, zinc sulfide,sodium aluminum sulfosilicates, cuprous oxide, and combinations thereof.

The paint composition may include an anti-fungal ingredient, suitably inan amount of about 0.1-5% by weight, or about 0.5-2.5% by weight.Anti-fungal agents prevent or inhibit mold growth resulting from lengthyexposure to wet or humid conditions. One suitable antifungal ingredientis cuprous oxide, sold by American Chemet Corporation under the nameLOLO TINT 97. Other suitable anti-fungal ingredients include withoutlimitation zinc oxide, cuprous sulfide, copper hydroxide, copper metal,and combinations thereof. A wide variety of known organic anti-fungalingredients can be used, but are less desirable due to the objective ofminimizing the organic components in the paint composition. Some of theinorganic pigments (e.g. cuprous oxide and zinc oxide) may serve as theanti-fungal ingredient and, if used as pigments, are present insufficient amounts.

The paint composition may include about 0.01-2% by weight, suitablyabout 0.01-1% by weight, of a synthetic or natural gum which iswater-soluble and serves as a thickening agent to help maintain thesolid ingredients in suspension. Suitable gums include withoutlimitation xanthan gum, guar gum, alginates, locust bean gum, andcombinations thereof.

In addition to minimizing the total amount of organic components,suitably to about 10% by weight or less, it is also desirable tominimize all other ingredients that might affect health, safety orenvironmental concerns. For example, the paint composition should besubstantially free, or totally free of Group I and Group II metaloxides.

The present invention also includes a method of coating a concrete ormasonry surface. The method includes the steps of providing awater-based paint composition which includes the ingredients statedabove in any of the amounts stated above. The paint composition includeswater, colloidal silica particles, an inorganic pigment, and a polymerbinder which constitutes not more than about 10% by weight of the paintcomposition. The method includes the steps of applying the water-basedpaint composition to a concrete or masonry surface, and evaporating thewater from the paint composition.

The present invention also includes a method of preparing a coatedconcrete or masonry surface. The method includes the steps of providinga concrete or masonry surface, providing a water-based paint compositionhaving the foregoing described ingredients in the foregoing amounts,applying the water-based paint composition to the concrete or masonrysurface, and evaporating the water from the paint composition. Thewater-based paint composition may include about 10-50% by weight water,about 5-40% by weight colloidal silica particles, about 40-85% by weightof an inorganic pigment, and about 1-10% by weight of a polymer binder.

Expressed another way, the method of preparing a coated concrete ormasonry surface includes the steps of providing a concrete or masonrysurface, coating the concrete or masonry surface with a water-basedpaint composition, and evaporating water from the paint composition todry the paint composition. The paint composition includes water,colloidal silica particles, an inorganic pigment and a polymer binder(suitably a styrene-acrylate polymer binder) in any of the amountsdescribed above, and may contain other ingredients as described above.

Example

A water-based paint composition was prepared by adding the followingingredients to a mixer in the stated order, and mixing them together toform a uniform blend. After all ingredients had been added, the mixingcontinued for at least ten additional minutes.

% By % Solids Ingredient Weight By Weight Aqueous Colloidal 29.99311.997 Silica (40% Solids) ACRONAL ® NX4627 5.999 2.880 (aqueous styreneacrylate copolymer, 48% solids) ALMATIS ® A-2 62.984 62.984 CalcinedAlumina (325 mesh, 44 microns diameter aluminum oxide) LOLO Tint 971.000 1.000 (cuprous oxide) KELZAN ® 0.025 0.025 Xanthan Gum TOTAL100.00 78.886

The paint composition was applied to a masonry surface on the side of abuilding where it was continuously exposed to sun, rain, wind, snow andhot and cold temperatures. After several months, the paint compositionshowed no signs of fading, peeling, eroding, molding or washing away.

The embodiments of the invention described herein are presentlypreferred. Various modifications and improvements can be made withoutdeparting from the spirit and scope of the invention. The scope of theinvention is indicated by the appended claims, and all changes that fallwithin the meaning and range of equivalents are intended to be embracedtherein.

We claim:
 1. A paint composition for coating concrete and masonrysurfaces, consisting essentially of: about 10-50% by weight water; about5-40% by weight colloidal silica particles; about 40-85% by weight of aninorganic pigment; about 1 to 9% by weight of a polymer binder selectedfrom the group consisting of polymers and copolymers of acrylic,acrylamide, vinyl ethers, vinyl esters, urethanes, methacrylates, andepoxy esters; and about 0.1-5% by weight cuprous oxide; wherein a sumtotal of all organic components does not exceed 9% by weight, inclusiveof the polymer binder, and the amounts are based on the total weight ofthe paint composition.
 2. The paint composition of claim 1, wherein thecolloidal silica particles have a particle size of about 4 to about 100nanometers.
 3. The paint composition of claim 1, wherein the inorganicpigment is selected from the group consisting of aluminum oxide, siliconoxide, titanium dioxide, zinc oxide, iron oxide, graphite, antimonyoxide, chromium oxide, cobalt aluminum oxide, zinc sulfide, sodiumaluminum sulfosilicates, cuprous oxide, and combinations thereof.
 4. Thepaint composition of claim 1, further comprising about 0.01-2% by weightof a synthetic or natural gum.
 5. The paint composition of claim 1,comprising about 10-30% by weight of the colloidal silica particles. 6.The paint composition of claim 1, wherein the composition issubstantially free of Group I and Group II metal oxides.
 7. The paintcomposition of claim 1, wherein the polymer binder comprises astyrene-acrylate copolymer.
 8. A paint composition for coating concreteand masonry surfaces, consisting essentially of: about 15-40% by weightwater; about 8-25% by weight colloidal silica particles; about 40-70% byweight of an inorganic pigment; about 2-8% by weight of a polymer binderselected from the group consisting of polymers and copolymers ofacrylic, acrylamide, vinyl ethers, vinyl esters, urethanes,methacrylates, and epoxy esters; and about 0.1-5% by weight cuprousoxide; wherein a sum total of all organic components does not exceed 9%by weight, inclusive of the polymer binder, and the amounts are based onthe total weight of the paint composition.
 9. The paint composition ofclaim 8, comprising about 0.5-2.5% by weight of the cuprous oxide. 10.The paint composition of claim 8, wherein the polymer binder comprises astyrene acrylate copolymer.
 11. The paint composition of claim 8,further comprising about 0.01-1% by weight of a synthetic or naturalgum.